1. Field of the Invention
This invention relates to a method and apparatus for rapid solidification of molten metal. More particularly, it relates to a casting wheel useful in the continuous casting of metallic filament.
2. Description of the Prior Art
In the production of glassy alloy continuous filaments, typically, an appropriate molten alloy is quenched at extreme quench rates, usually at least about 10.sup.4 .degree. C./sec. by extruding the molten alloy from a pressurized reservoir through an extrusion nozzle onto a high speed rotating quench surface as is representatively shown in U.S. Pat. No. 4,142,571 for "Continuous Casting Method for Metallic Strips" issued Mar. 6, 1978 to Narasimhan, hereby incorporated by reference. Such filaments are necessarily thin, typically about 25 to 100 microns, due to the extreme heat transfer rate required to prevent substantial crystallization, though considerable selectivity may be exercised respecting the transverse dimensions and cross-section of the filament.
Casting wheels of the prior art generally have been cooled by spraying a fluid, usually water, onto the inner surface of the wheel. However, such spray-cooled wheels do not provide sufficiently uniform cooling along the wheel quench surface. Casting wheels of the prior art have also been cooled by forcing a coolant to flow through separate discrete passages which are drilled axially through a portion of the wheel and located about the periphery of the casting wheel near the wheel quench surface. Such a casting wheel is representatively shown in U.S. Pat. No. 4,307,771 for "Forced-Convection-Cooled Casting Wheel" issued Dec. 29, 1981, to Draizen, et al., the disclosure of which is hereby incorporated by reference thereto. The casting wheel has an internal stiffening section which is particularly effective in preventing crowning-type distortions of the quench surface, which can be significant when casting relatively wide filaments of material. The casting wheel of Draizen, et al., however, is rather expensive, and impractical for use in casting narrow ribbons less than about 0.20 cm in width where crowning is generally not a problem. In addition, prior art casting wheels have no satisfactory means for adjusting the size of the cooling passages to accommodate different alloy compositions, and have undesireable circumferential temperature variations along the wheel quench surface caused by the presence of separate coolant passageways.